1. Field of the Invention
The present invention relates to a sheet-handling device mounted on the body of an image-forming machine such as an electrostatic copier or a printer, to handle a sheaf of sheets formed by being introduced from the body of the image-forming machine or, more concretely, to handle the sheets, such as sorting, stapling and punching, and, then, to discharge the sheets onto a discharge tray for sorting.
2. Description of the Prior Art
A sheet-handling device mounted on the body of a copier is generally so constituted as to convey the sheets introduced from the body of the copier to an intermediate tray, form a sheaf of sheets on the intermediate tray, and discharge the sheets onto a discharge tray for sorting. While the sheet is being handled to form a sheaf of sheets on the intermediate tray, it is not allowed to convey the succeeding sheet into the intermediate tray. During this period, therefore, the copying operation of the copier must be discontinued. Discontinuation of the copying operation not only decreases the production efficiency of the sheet-handling device but also decreases the production efficiency of the whole system inclusive of the copier.
Sheet-handling devices aimed at overcoming a decrease in the production efficiency have already been proposed as taught in, for example, Japanese Patent No. 2541979, JP-B-06-099070 and JP-A-09-235069.
A sheet-handling device disclosed in Japanese Patent No. 2541979 is so constituted as to have a sheet discharged from an image-forming machine stay in a conveyer passage by controlling conveyer means while a stapler is executing the stapling. What is aimed at by this device is to minimize or eliminate the loss time in the image-forming operation even when the sheets are being stapled on a tray. In this device, however, only a piece of sheet is allowed to stay in the conveyer passage while the stapler is executing the stapling, but the second and subsequent sheets cannot be conveyed causing, therefore, the image-forming operation to be discontinued.
A sheet-handling device disclosed in JP-B-06-099070 includes first and second sheet conveyer paths for guiding the sheet to a sheet-handling tray, and change-over means which is so changed over that the sheet is sent into either the first sheet conveyer path or the second sheet conveyer path. The first and second sheets are sent into the second and first sheet conveyer paths so as to stay therein by changing over the change-over means even while the sheet-handling means is executing the sheet-handling operation for the sheaf of sheets on the handling tray. After the sheet handling has been finished, the first and second sheets are sent in an overlapped state onto the sheet-handling tray. What is aimed at by this device is to eliminate the loss time and, hence, to improve the productivity by feeding the sheets without waiting time. However, this device must be provided with change-over means for standing by in addition to the two sheet conveyer paths, resulting in an increase in the size of the constitution and in the cost, and making it difficult to cope with the jamming. Besides, up to two pieces of sheets are permitted to stand by. Three pieces can be made to stand by requiring, however, the provision of three sheet conveyer paths, which results in a further increase in the size of the constitution and in the cost, and making it further difficult to cope with the jamming.
A sheet-handling device disclosed in JP-A-09-235069 includes first and second introduction passages for guiding the sheet discharged from an image-forming machine into a sheet conveyer passage prior to introducing the sheet to an intermediate stacker, change-over means for changing over the inlet of either the first introduction passage or the second introduction passage, and a pair of conveyer rollers for conveying, into the intermediate stacker, the two pieces of sheets conveyed from the first and second introduction passages in a state of being overlapped one upon the other with their ends being abut. What is aimed at by this device is to efficiently convey the sheet to improve the productivity without delaying or interrupting the formation of image by the image-forming machine and the continuous discharge of the paper between the preceding handling of the sheaf of sheets and the subsequent handing-over of the sheaf of sheets. However, this device must be provided with two introduction passages and change-over means in addition to the sheet conveyer passage causing the constitution to become complex and making it difficult to cope with the jamming. Besides, only two pieces of sheets are permitted to stand by.